The Smart Roadster 698cc engine is one of the most characterful powerplants ever fitted to a production sports car. Tiny in displacement, turbocharged from the factory, and mounted mid-rear behind the seats, this three-cylinder unit punches well above its weight — yet it remains widely misunderstood, even by people who own one. Whether you are shopping for a Roadster, troubleshooting a fault, or planning a performance build, understanding exactly what is under that rear clamshell is essential. This guide covers the engine’s architecture, its four factory variants, the turbocharger system, known weak points, and the genuine performance headroom available to those willing to extract it.
Architecture and Origins: What Actually Lives Behind the Seats
The Smart Roadster’s engine is a 698cc, three-cylinder, turbocharged, water-cooled unit derived from a Mitsubishi design and produced under licence by Smart parent company DaimlerChrysler. It shares its basic block architecture with the engine used in the Smart Forfour and, before that, the city car Smart ForTwo (W450). However, the Roadster’s application is meaningfully different: it is mounted transversely in a mid-rear position, directly behind the passenger compartment, driving the rear wheels through Smart’s Softouch automated-manual gearbox.
The bore is 66.5 mm and the stroke 67.0 mm, giving an almost perfectly square configuration. The cylinder head features a twin-cam, twelve-valve layout (two inlet, two exhaust per cylinder), with a compression ratio of 9.5:1 on the standard turbocharged variants. Displacement of just 698cc is compensated for by forced induction: every production Roadster engine is turbocharged. There is no naturally aspirated version in the 452 Roadster lineup.
One point worth stating clearly: the front compartment of the Smart Roadster is luggage space only. If someone tells you the engine is at the front, they are mistaken. The mid-rear layout gives the car genuinely favourable weight distribution and is central to its handling character — as anyone who has explored how the Roadster’s chassis responds to suspension adjustments will already appreciate.
The Four Engine Variants: Outputs, Differences and Which to Buy
Smart produced four distinct power outputs from the same basic 698cc block across the Roadster’s production life from 2003 to 2006. Understanding the differences is critical when buying or building.
45kW Lite — Avoid
The entry-level variant produces 61 bhp and around 90 Nm of torque, running boost pressure of approximately 0.89 bar. The critical omission is the absence of an oil cooler. Without adequate oil temperature management, the 45kW engine is significantly more prone to premature wear, oil burning, and in severe cases, internal failure under sustained load. This variant is the one to avoid unless the price is extremely low and you are aware of the elevated risk. The oil burning tendency is well documented and is explained in detail in our guide on why the 45kW is particularly susceptible to oil consumption problems.
60kW Standard — The Sweet Spot
The 60kW (82 bhp) unit is the most common and most desirable everyday variant. It runs 1.09 bar of boost and, crucially, includes an oil cooler as standard. This single hardware difference makes the 60kW considerably more robust in real-world use. Torque is approximately 110 Nm, delivered in a narrow but entertaining band. If you are buying a Roadster for road use and moderate performance, the 60kW is the correct choice.
66kW SB2 Brabus — Enthusiast Pick
Produced in collaboration with Brabus, the SB2 variant pushes boost to 1.33 bar, delivering 90 bhp and around 130 Nm. It includes Brabus-specific ECU calibration and benefits from the oil cooler and strengthened ancillaries of the 60kW platform. A genuinely more sporting experience on road.
74kW Full Brabus — The Factory Hot Rod
The range-topping Brabus at 74kW (101 bhp) runs 1.43 bar of boost and represents the absolute limit of what Smart and Brabus were comfortable delivering on a standard internal drivetrain. Torque peaks at approximately 150 Nm. These are rarer, command a price premium, and are the most rewarding to drive in standard form — though tuners often note that the factory calibration still leaves room on the table.
The Turbocharger: Garrett 1238S and Pneumatic Wastegate
All Roadster variants share the same fundamental forced induction hardware: a Garrett 1238S fixed-geometry turbocharger with a pneumatic wastegate. The compressor wheel is small by modern standards, which produces rapid spool-up — lag is noticeable but modest — and a sharp, characterful power delivery once the boost comes in.
The wastegate is controlled by the Bosch MEG 1.1 ECU, which uses a solenoid-modulated pneumatic signal to regulate boost pressure. This means boost levels are directly adjustable through ECU calibration, within the limits of what the turbocharger and internals can physically support. The relationship between wastegate control, manifold pressure and the torque curve is not linear, and how boost pressure actually translates into torque on this engine is worth understanding before making any tuning decisions.
The Garrett 1238S is a robust unit that rarely fails on its own merits. Problems attributed to the turbo are more commonly oil-related: coking of the bearing journal caused by hot shutdowns without an adequate cool-down period, or contamination from an engine that has been burning oil. Proper oil specification and regular changes are the best turbo insurance policy available.
The ECU: Bosch MEG 1.1 and Firmware
Engine management on every Smart Roadster is handled by the Bosch MEG 1.1 ECU. This unit controls fuelling, ignition timing, boost pressure targeting, idle, cold-start enrichment, and all associated engine protection strategies. The best firmware version for tuning purposes is 1037371568, which offers the most refined base calibration and the broadest compatibility with aftermarket mapping tools.
The ECU communicates over a proprietary variant of the CAN bus architecture. Standard OBD2 dongles often return partial data or fail to access live engine parameters correctly — an important consideration if you are diagnosing a fault or monitoring boost. Our compatibility guide for OBD2 scanners on the Smart Roadster covers which tools actually work and which ones do not.
The EEPROM on the MEG 1.1 is 256 bytes, containing key adaptation values including idle learn data and injector trims. These are reset whenever the ECU is flashed, which means a proper idle relearn procedure is required after any remap. Ignoring this step is a common cause of rough idling complaints following ECU work.
Cylinder Head, Breathing and the Case for Flow Work
Given the small displacement, the cylinder head is disproportionately important on the 698cc engine. The factory head is a competent piece of engineering for its brief, but its ports are conservative and its valve sizes modest. At higher boost levels — particularly on remapped engines targeting 100 bhp or beyond — the head becomes a meaningful restriction.
The inlet ports benefit from matched porting to smooth the transition from the inlet manifold, while the exhaust ports respond well to bowl blending around the valve seat. Flow bench testing consistently shows worthwhile gains, particularly on the exhaust side where the factory finish is rougher. The cylinder head also houses the coolant passages that feed the turbocharger’s water-cooled bearing housing, so any head work must preserve these galleries. If you are considering head modifications, our detailed article on porting and flow work for the Smart Roadster cylinder head is the logical next step.
Known Weak Points and Long-Term Reliability
For a small turbocharged engine that is now approaching twenty years old, the 698cc unit has a reasonable reliability record — provided it has been maintained correctly. The most common failure modes are as follows:
- Oil burning and bore wear — predominantly on the 45kW Lite due to the absent oil cooler, but any engine neglected on oil changes can develop this.
- Turbocharger journal wear — caused by hot shutdowns, extended idling with poor oil, or oil contamination. Early signs include a faint whine at boost.
- Head gasket failure — uncommon on standard-power engines but a genuine risk on heavily boosted or overheated units. Coolant loss with no external leak is the warning sign.
- Coking of the variable-geometry actuator — not applicable here (fixed geometry unit), but oil vapour accumulation in the inlet tract is common and should be addressed with a catch can.
- Coolant system neglect — the thermostat and coolant temperature sensor are inexpensive parts that cause outsized problems when they fail silently. Regular coolant changes (every two years) are non-negotiable.
The engine’s longevity is also closely tied to gearbox health. The Softouch automated manual puts specific demands on the clutch, and a slipping or dragging clutch generates heat that the entire drivetrain absorbs. For those considering drivetrain work alongside engine maintenance, understanding what a clutch replacement on the Roadster actually involves gives useful context on how integrated the rear drivetrain components are.
Performance Potential: How Far Can the 698cc Go?
The Smart Roadster 698cc engine has considerably more in reserve than the factory numbers suggest. The Garrett 1238S turbocharger is capable of supporting outputs well beyond the factory 74kW Brabus peak, and the bottom end is surprisingly robust when oil maintenance is respected. ECU remapping is the most cost-effective route to unlocking this potential.
At smartroadster.tech we offer four map tiers built specifically for this engine: BASIC at 90 bhp, PLUS at 100 bhp, PRO at 110 bhp, and EVOLUTION at 125 bhp. Each map is calibrated to work within the physical limits of the hardware at that level — the EVOLUTION map, for instance, assumes uprated intercooling and appropriate fuelling support. Beyond 125 bhp, the turbocharger and injector sizing become the primary constraints, at which point hardware upgrades are necessary rather than optional. You can explore the full details of what each performance mapping package includes and which variants are compatible.
External reference points for the turbocharger’s flow capacity and compressor maps are available through Garrett Motion’s turbocharger technical resources, which help contextualise where the 1238S sits relative to its maximum efficiency island. For a deeper understanding of how small-displacement forced induction engines behave thermodynamically, the Wikipedia article on turbocharger operating principles provides a solid foundation. Those interested in the relationship between boost and combustion stability should also consult the reference on air-fuel ratio, which underpins every fuelling decision made during calibration.
Summary: Understanding Your Smart Roadster 698cc Engine
The Smart Roadster 698cc engine explained in full reveals a unit that is cleverly engineered, genuinely tuneable, and rewarding to maintain correctly. Choose the 60kW or above for reliability, respect the oil cooling system, keep the turbo healthy with proper oil changes, and you have a powerplant capable of delivering real entertainment. For those who want more, the remapping headroom is substantial — and unlike many older cars, the Bosch MEG 1.1 ECU is well understood and directly accessible. Start with the fundamentals, understand what you have, and the 698cc will repay the attention.
